1. Field of the Invention
The present invention is directed generally to wireless communication systems and, more specifically, to the transmission of control information signals in an uplink of a communication system.
2. Description of the Art
A communication system includes a DownLink (DL) that conveys transmission signals from a Base Station (BS or Node B) to User Equipments (UEs), and an UpLink (UL) that conveys transmission signals from UEs to the Node B. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A Node B is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), an access point, or some other equivalent terminology.
More specifically, the UL supports the transmission of data signals carrying information content, control signals providing information associated with the transmission of data signals in the DL, and Reference Signals (RSs), which are commonly referred to as pilot signals. The DL also supports the transmission of data signals, control signals, and RSs.
UL data signals are conveyed through a Physical Uplink Shared CHannel (PUSCH) and DL data signals are conveyed through a Physical Downlink Shared CHannel (PDSCH).
In the absence of a PUSCH transmission, a UE conveys Uplink Control Information (UCI) through a Physical Uplink Control CHannel (PUCCH). However, when there is a PUSCH transmission, the UE may convey UCI together with data information through the PUSCH.
DL control signals may be broadcast or sent in a UE-specific nature. Accordingly, UE-specific control channels can be used, among other purposes, to provide UEs with Scheduling Assignments (SAs) for PDSCH reception (DL SAs) or PUSCH transmission (UL SAs). The SAs are transmitted from the Node B to respective UEs using Downlink Control Information (DCI) formats through respective Physical Downlink Control CHannels (PDCCHs).
The UCI includes ACKnowledgment (ACK) information associated with the use of a Hybrid Automatic Repeat reQuest (HARQ) process. The HARQ-ACK information is sent in response to the reception of Transport Blocks (TBs) by the UE, conveyed by the PDSCH.
The UCI may also include a Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), or a Rank Indicator (RI), which may be jointly referred to as Channel State Information (CSI). The CQI provides the Node B with a measure of the Signal to Interference and Noise Ratio (SINR) the UE experiences over sub-bands or over the whole operating DL BandWidth (BW). This measure is typically in the form of the highest Modulation and Coding Scheme (MCS) for which a predetermined BLock Error Rate (BLER) can be achieved for the transmission of TBs. The MCS represents the product of the modulation order (number of data bits per modulation symbol) and of the coding rate applied to the transmission of data information. The PMI/RI informs the Node B how to combine the signal transmission to the UE from multiple Node B antennas using a Multiple-Input Multiple-Output (MIMO) principle.
FIG. 1 illustrates a conventional PUSCH transmission structure.
Referring to FIG. 1, for simplicity, the Transmission Time Interval (TTI) is one sub-frame 110, which includes two slots. Each slot 120 includes NsymbUL symbols used for the transmission of data signals, UCI signals, or RSs. Each symbol 130 includes a Cyclic Prefix (CP) to mitigate interference due to channel propagation effects. The PUSCH transmission in one slot 120 may be either at a same or different BW as the PUSCH transmission in the other slot.
Some symbols in each slot are used to a transmit RS 140, which enables channel estimation and coherent demodulation of the received data and/or UCI signals.
The transmission BW includes frequency resource units that will be referred to herein as Physical Resource Blocks (PRBs). Each PRB includes NscRB sub-carriers, or Resource Elements (REs), and a UE is allocated MPUSCH PRBs 150 for a total of MscPUSCH=MPUSCH·NscRB REs for the PUSCH transmission BW.
The last sub-frame symbol is used for transmitting a Sounding RS (SRS) 160 from one or more UEs. The SRS provides the Node B with a CQI estimate for the UL channel medium for the respective UE. The SRS transmission parameters are semi-statically configured by the Node B to each UE through higher layer signaling such as, for example, Radio Resource Control (RRC) signaling.
In FIG. 1, the number of sub-frame symbols available for data transmission is NsymbPUSCH=2·NsymbUL−1)−NSRS, where NSRS=1 if the last sub-frame symbol is used for SRS transmission and NSRS=0 otherwise.
FIG. 2 illustrates a conventional transmitter for transmitting data, CSI, and HARQ-ACK signals in a PUSCH.
Referring to FIG. 2, coded CSI bits 205 and coded data bits 210 are multiplexed by multiplexer 220. HARQ-ACK bits are then inserted by puncturing data bits and/or CSI bits by puncturing unit 230. The Discrete Fourier Transform (DFT) is then performed by the DFT unit 240. REs are then selected by sub-carrier mapping by the sub-carrier mapping unit 250 corresponding to the PUSCH transmission BW from controller 255. Inverse Fast Fourier Transform (IFFT) is performed by an IFFT unit 260, CP insertion is performed by a CP insertion unit 270, and time windowing is performed by filter 280, thereby generating a transmitted signal 290.
The PUSCH transmission is assumed to be over clusters of contiguous REs in accordance to the DFT Spread Orthogonal Frequency Division Multiple Access (DFT-S-OFDMA) method for signal transmission over one cluster 295A (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA)), or over multiple non-contiguous clusters 295B.
FIG. 3 illustrates a conventional receiver for receiving a transmission signal as illustrated in FIG. 2.
Referring to FIG. 3, an antenna receives a Radio-Frequency (RF) analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not shown for brevity, the received digital signal 310 is filtered by filter 320 and the CP is removed by CP removal unit 330. Subsequently, the receiver unit applies a Fast Fourier Transform (FFT) by an FFT unit 340, selects the REs used by the transmitter by sub-carrier de-mapping by a sub-carrier demapping unit 350 under a control of controller 355. Thereafter, an Inverse DFT (IDFT) unit 360 applies IDFT, an extraction unit 370 extracts the HARQ-ACK bits, and a de-multiplexing unit 380 demultiplexes the data bits 390 and CSI bits 395.
The RS transmission is assumed to be through a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence. An example of CAZAC sequences is shown in Equation (1).
                                          c            k                    ⁡                      (            n            )                          =                  exp          ⁡                      [                                                            j                  ⁢                                                                          ⁢                  2                  ⁢                  π                  ⁢                                                                          ⁢                  k                                L                            ⁢                              (                                  n                  +                                      n                    ⁢                                                                  n                        +                        1                                            2                                                                      )                                      ]                                              (        1        )            
In Equation (1), L is a length of the CAZAC sequence, n is an index of an element of the sequence n={0, 1, . . . , L−1}, and k is an index of the sequence. If L is a prime integer, there are L−1 distinct sequences defined as k ranges in {0, 1, . . . , L−1}.
For an even number of REs, CAZAC-based sequences with even length can be generated, e.g., by truncating or extending a CAZAC sequence.
Orthogonal multiplexing of CAZAC sequences can be achieved by applying different Cyclic Shifts (CSs) to the same CAZAC sequence.
For HARQ-ACK or RI transmission in the PUSCH, a UE determines the respective number of coded symbols Q′ as shown in Equation (2).
                              Q          ′                =                  min          ⁡                      (                                          ⌈                                                      O                    ·                                          β                      offset                      PUSCH                                                                                                  Q                      m                                        ·                    R                                                  ⌉                            ,                              4                ·                                  M                  sc                  PUSCH                                                      )                                              (        2        )            
In Equation (2), O is a number of HARQ-ACK information bits or RI information bits, βoffsetPUSCH is informed to the UE through RRC signaling, Qm is a number of data bits per modulation symbol (Qm=2, 4, 6 for QPSK, QAM16, QAM64, respectively), R is a data code rate of an initial PUSCH transmission for the same TB, MscPUSCH is a PUSCH transmission BW in a current sub-frame, and ┌ ┐ indicates a ceiling operation that rounds a number to its next integer.
The data code rate R is defined as shown in Equation (3).
                    R        =                              (                                          ∑                                  r                  =                  0                                                  C                  -                  1                                            ⁢                              K                r                                      )                    /                      (                                          Q                m                            ·                              M                sc                                  PUSCH                  ⁢                                      -                                    ⁢                  initial                                            ·                              N                symb                                  PUSCH                  ⁢                                      -                                    ⁢                  initial                                                      )                                              (        3        )            
In Equation (3), C is a total number of data code blocks and Kr is a number of bits for data code block number r. The maximum number of HARQ-ACK or RI REs is limited to the REs of 4 DFT-S-OFDM symbols (4·MscPUSCH).
When the UE receives one TB, the HARQ-ACK includes 1 bit that is encoded as a binary ‘1’, if the TB is correctly received (positive acknowledgement or ACK), or as a binary ‘0’, if the TB is incorrectly received (negative acknowledgment or NACK).
When the UE receives two TBs, the HARQ-ACK includes 2 bits [o0ACK o1ACK] with o0ACK for TB 0 and o1ACK for TB 1. The encoding for the HARQ-ACK bits is given in Table 1 below, where o2ACK=(o0ACK+o1ACK)mod 2 to provide a (3, 2) simplex code for the 2-bit HARQ-ACK transmission.
TABLE 1Encoding for 1-bit and 2-bits of HARQ-ACKEncodedQmHARQ-ACK - 1 bitEncoded HARQ-ACK - 2 bits2[o0ACK y][o0ACK o1ACK o2ACK o0ACK o1ACK o2ACK]4[o0ACK y x x][O0ACK O1ACK X X O2ACK O0ACK X X O1ACK O2ACK X X]6[o0ACK y x x x x][o0ACK o1ACK x x x x o2ACK o0ACK x x x x o1ACK o2ACK x x x x]
For CQI/PMI multiplexing in a PUSCH, a UE determines a respective number of coded symbols Q′ as shown in Equation (4).
                              Q          ′                =                  min          ⁡                      (                                          ⌈                                                                            (                                              O                        +                        L                                            )                                        ·                                          β                      offset                      PUSCH                                                                                                  Q                      m                                        ·                    R                                                  ⌉                            ,                                                                    M                    sc                    PUSCH                                    ·                                      N                    symb                    PUSCH                                                  -                                                      Q                    RI                                                        Q                    m                                                                        )                                              (        4        )            
In Equation (4), O is a number of CQI/PMI information bits, L is a number of CRC bits given by
  L  =      {                            0                                      O            ≤            11                                                8                                      otherwise            ,                              and QCQI=Q·Q′. If RI is not transmitted, then QRI=0.
For CQI/PMI channel coding, convolutional coding is used, if O>11 bits, and (32, O) Reed-Mueller (RM) block coding is used, if O≦11 bits. The code words of the (32, O) block code are a linear combination of the 11 basis sequences denoted by Mi,n and given in Table 2 below. Denoting the input sequence by o0, o1, o2, . . . , oO−1 and the encoded CQI/PMI block by b0, b1, b2, b3, . . . , bB−1, B=32, it is
            b      i        =                  ∑                  n          =          0                          O          -          1                    ⁢                        (                                    o              n                        ·                          M                              i                ,                n                                              )                ⁢        mod        ⁢                                  ⁢        2              ,i=0, 1, 2, . . . , B−1.
The output sequence q0, q1, q2, q3, . . . , qQCQI−1 is obtained by circular repetition of the encoded CQI/PMI block as qi=b(i mod B), i=0, 1, 2, . . . , QCQI−1.
TABLE 2Basis sequences for (32, O) code.iMi,0Mi,1Mi,2Mi,3Mi,4Mi,5Mi,6Mi,7Mi,8Mi,9Mi,100110000000011111000000112100100101113101100001014111100010015110010111016101010101117100110011018110110010119101110100111010100111011111110011010112100101011111311010101011141000110100115110011110111611101110010171001110010018110111110001910000110000201010001000121110100000112210001001101231110100011124111110111102511000111001261011010011027111101011102810101110100291011111110030111111111113110000000000
Among the UCI, HARQ-ACK has the highest reliability requirements and the respective REs are located next to the RS in each slot in order to obtain the most accurate channel estimate for their demodulation. When there is no CQI/PMI transmission, RI is placed at the symbols after the HARQ-ACK, while CQI/PMI transmission is uniformly multiplexed throughout the sub-frame.
FIG. 4 illustrates conventional UCI multiplexing in a PUSCH sub-frame.
Referring to FIG. 4, the HARQ-ACK bits 410 are placed next to the RS 420 in each slot of the PUSCH sub-frame. The CQI/PMI bits 430 are multiplexed across all DFT-S-OFDM symbols and the remaining of the sub-frame carries transmission of data bits 440. As the multiplexing is prior to the DFT, a virtual frequency dimension is used for the UCI placement.
For a UE transmitter having more than one antenna, Transmission Diversity (TxD) can enhance the reliability of the received signal by providing spatial diversity.
An example TxD method is Space Time Block Coding (STBC). With STBC, if the first antenna transmits the symbols d0,d1, the second antenna transmits the symbols d1*,−d*0, where d* is the complex conjugate of d. Denoting the channel estimate for the signal received at a reference Node B antenna and transmitted from the jth UE antenna by hj, j=1, 2, and denoting the signal received at the Node B antenna in the kth DFT-S-OFDM symbol by yk, k=1, 2, the decision for a pair of STBC symbols [{circumflex over (d)}k,{circumflex over (d)}k+1] is according to [{circumflex over (d)}k,{circumflex over (d)}k+1]T=HH[yk,yk+1*]T, where [ ]T denotes the transpose of a vector and
      H    H    =            [                                                                  h                1                *                            -                              h                2                                                                                                        h                2                *                            ⁢                                                          ⁢                              h                1                                                        ]        /                  (                                                                          h                1                                                    2                    +                                                                  h                2                                                    2                          )            .      
In order to increase the supportable data rates, aggregation of multiple Component Carriers (CCs) is considered in both the DL and the UL to provide higher operating BWs. For example, to support communication over 60 MHz, aggregation of three 20 MHz CCs can be used.
FIG. 5 illustrates the concept of conventional Carrier Aggregation (CA).
Referring to FIG. 5, an operating DL BW of 60 MHz 510 is constructed by the aggregation of 3 (contiguous, for simplicity) DL CCs 521, 522, and 523, each having a BW of 20 MHz. Similarly, an operating UL BW of 60 MHz 530 is constructed by the aggregation of 3 UL CCs 541, 542, and 543, each having a BW of 20 MHz. For simplicity, in the example illustrated in FIG. 5, each of DL CCs 521, 522, and 523 is assumed to be uniquely mapped to a UL CC (symmetric CA), but it is also possible for more than 1 DL CC to be mapped to a single UL CC or for more than 1 UL CC to be mapped to a single DL CC (asymmetric CA, not shown for brevity). The link between DL CCs and UL CCs is typically UE-specific.
The Node B configures CCs to a UE using RRC signaling. Assuming transmission of different TBs in each of the multiple DL CCs 521, 522, and 523, multiple HARQ-ACK bits will be transmitted in the UL.
For simultaneous HARQ-ACK and PUSCH transmissions, the direct extension of the conventional operation is to include the HARQ-ACK bits for the TBs received in a DL CC in the PUSCH of its linked UL CC. However, in practice, not all UL CCs may have PUSCH transmissions in the same sub-frame. Therefore, any design supporting transmission in the PUSCH of HARQ-ACK bits corresponding to reception of TBs in multiple DL CCs should consider the case of only a single PUSCH. This also applies for any UCI type (not just HARQ-ACK). The PUCCH transmission is assumed to be in a single UL CC, which will be referred to as UL Primary CC.
TxD should be supported for UCI transmission in the PUSCH (if the UE has multiple transmitter antennas), particularly for the HARQ-ACK that requires high reliability that may be difficult to achieve without substantially increasing the required PUSCH resources particularly for large HARQ-ACK payloads (such as, for example, 10 HARQ-ACK bits corresponding to reception of TBs in 5 DL CCs with 2 TBs per DL CC).
Therefore, there is a need to support transmission of HARQ-ACK information in the PUSCH in response to the reception of at least one TB from a UE configured with CA in the DL of a communication system.
There is another need to dimension the PUSCH resources used for HARQ-ACK multiplexing depending on the HARQ-ACK coding method in order to improve the HARQ-ACK reception reliability.
There is another need to select the PUSCH for the transmission of UCI, for multiple simultaneous PUSCH transmissions.
There is another need to support TxD for the HARQ-ACK transmission in the PUSCH.